The present invention relates generally to providing a casing exit for a lateral borehole, and more particularly to systems and methods for providing a casing exit with little or no milling of the casing.
Hydrocarbons can be produced through relatively complex wellbores traversing a subterranean formation. Some wellbores can include multilateral wellbores and/or sidetrack wellbores. Multilateral wellbores include one or more lateral wellbores extending from a parent (or main) wellbore. A sidetrack wellbore is a wellbore that is diverted from a first general direction to a second general direction. A sidetrack wellbore can include a main wellbore in a first general direction and a secondary wellbore diverted from the main wellbore in a second general direction. A multilateral wellbore can include one or more windows or casing exits to allow corresponding lateral wellbores to be formed. A sidetrack wellbore can also include a window or casing exit to allow the wellbore to be diverted to the second general direction.
The casing exit for either multilateral or sidetrack wellbores can be formed by positioning a casing joint and a whipstock in a casing string at a desired location in the main wellbore. The whipstock is used to deflect one or more mills laterally (or in an alternative orientation) relative to the casing string. The deflected mill(s) machines away and eventually penetrates part of the casing joint to form the casing exit in the casing string. Drill bits can be subsequently inserted through the casing exit in order to cut the lateral or secondary wellbore.
Milling the casing exit is a time consuming and potentially harmful process. Milling away the material of the casing creates highly abrasive metallic chips that can cause significant wear on equipment located in the wellbore during the milling process and on equipment that subsequently passes through the area in which the milling takes place. Furthermore, because the mill is only used for milling the casing exit, several trips down the wellbore are required before commencing actual drilling of the associated lateral wellbore.